The present invention relates to an interactive graphic system for the mathematical representation of physical models by digitation of surfaces and computer aided design (CAD) of the parts outside the figure or not available on the model.
As is known, particularly in the fashion, model making and mold-making sectors, there is the problem of obtaining a program for controlling a machine tool, for example for working a molded item with numerically controlled grinders, directly from a model of the workpiece to be produced. If the model is constituted by a physical reproduction of the workpiece the program must be generated by digitation of the model itself; in this case the fundamental requirement is to obtain a rapid and reliable digitation. A typical processing requirement of the program is that of obtaining the two halves (die and matrix) of the mold directly from a single digitation of the model.
The available known techniques for use are the copy grinding method, the detection and recording method, and the digitation with measuring machine method; all these methods, however, have disadvantages, which limit the advantages of use, in fact:
the copy grinding method, while having the advantage of not requiring any dedicated digitising apparatus in that the scanning feeler directly controls the grinder, has the disadvantage of producing only a single shape for each scan of the model, of having a grinding speed limited by the lower scanning speed imposed by the feeler, of having a reduction in the scanning precision caused by the vibrations induced by working, and of not being able to compensate the form and errors of the feeler because the working is in line with the detection phase; finally it is necessary to change the tool tip and repeat the model scanning process at each working stage;
the detection and recording method also utilizes a copying grinder as the basic machine, but the process is divided into two parts: digitation and working; a control unit in fact controls the first part of the process, namely digitation of the model utilizing the grinder and its feeler at a speed allowed by the feeler itself, and the result is recorded on a disc; subsequently the same unit controls the machine in the grinding phase at the maximum speed allowed by the machine tool using the previously recorded data; in this case the scanning phase represents about 20-30% of the overall process time and the detection of the model must be repeated in the various working phases (roughing out, semi-finishing and finishing); the use of the grinder for scanning the model, taking it away from working, is however inefficient and uneconomic;
the digitation with measuring machine method utilises a dedicated machine for generating a the model and generates a program for controlling several grinders, the scan data is processed by a processor which optimizes the cutting paths and derives programs for roughing out, semi-finishing and finishing from the same set of scan data, and the same measuring machine can be utilized for dimensionally controlling the working results; this method obtains the maximum use of the machine tool which can work full time and at maximum efficiency: the main limitations consist in; the low digitation speed due to the necessity of detecting all the points required for the precise control of the grinder in the finishing phase, and by the necessity of rotating the feeler; the cost of the system due to the dimensions of the machine and the configuration of the feelers; the low precision due to the impossibility of compensating for the spacial dimensions of the feeler; and the relative incompleteness of the process, which permits only the data derived from the physical model to be processed (this limitation is however shared with the other methods described above).
Moreover there is a further limitation with these three methods due to the fact that they can only generate programs for the grinder on three axes, and not on five axes which, on the other hand, would allow a faster operating speed and a better finish.